SmogRank / United States / South Dakota / Watertown
Watertown, month by month
Watertown has a measured daily mean on 1,211 days since 1 January 2023. Its worst month was June 2023, at 62 US AQI (14.8 µg/m³), 389th of 1,603 cities on that month's world ranking. Its cleanest was September 2026, at 22 US AQI (3.9 µg/m³). 2025 averaged 43 US AQI (7.7 µg/m³), against 43 US AQI (7.8 µg/m³) in 2024.
Every month since 2023
The US EPA's Air Quality Index for PM2.5 (2024 breakpoints). Show values as: µg/m³ · US AQI · India AQI · China AQI · European AQI · UK DAQI · Canada AQHI+. About the scales
Months without a mean, and why
9 months
| Month | Why |
|---|---|
| Feb 2026 | 5 of 28 days measured; a month needs 20. The others: 23 with under 18 hours of readings or readings that failed our checks. |
| Dec 2025 | 17 of 31 days measured; a month needs 22. The others: 14 with under 18 hours of readings or readings that failed our checks. |
| Nov 2025 | 6 of 30 days measured; a month needs 21. The others: 24 with under 18 hours of readings or readings that failed our checks. |
| Oct 2025 | 21 of 31 days measured; a month needs 22. The others: 10 with under 18 hours of readings or readings that failed our checks. |
| Jan 2025 | 17 of 31 days measured; a month needs 22. The others: 14 with under 18 hours of readings or readings that failed our checks. |
| Dec 2024 | 17 of 31 days measured; a month needs 22. The others: 14 with under 18 hours of readings or readings that failed our checks. |
| Aug 2024 | 20 of 31 days measured; a month needs 22. The others: 11 with under 18 hours of readings or readings that failed our checks. |
| Jan 2024 | 20 of 31 days measured; a month needs 22. The others: 11 with under 18 hours of readings or readings that failed our checks. |
| Oct 2023 | 20 of 31 days measured; a month needs 22. The others: 11 with under 18 hours of readings or readings that failed our checks. |
A day counts once 18 hours of it are measured; a month needs 70% of its days.
Watertown's worst months
| Month | US AQI | World rank | Episode |
|---|---|---|---|
| June 2023 | 6214.8 µg/m³ | 389thof 1,603 | Eastern United States and Canada, June and July 2023 United States and Canada, June 2023 |
| September 2023 | 5913.2 µg/m³ | 250thof 2,176 | Northern United States and Canada, August and September 2023 |
| May 2023 | 5813.1 µg/m³ | 207thof 1,600 | Northern United States and Canada, May 2023 |
| July 2023 | 5813.1 µg/m³ | 275thof 1,432 | United States and Canada, July 2023 Eastern United States and Canada, June and July 2023 |
| August 2023 | 5812.6 µg/m³ | 294thof 1,980 | Northern United States and Canada, August and September 2023 Northern United States, August 2023 |
| July 2024 | 5511.0 µg/m³ | 564thof 2,566 | – |
Monthly means over the days measured; finished months only. World rank: its place on that month's world ranking of every city with enough days. Each month opens that ranking.
Watertown's worst days
| Day | US AQI | Episode |
|---|---|---|
| 18 May 2023 | 17082.8 µg/m³ | Northern United States and Canada, May 2023 |
| 1 Jun 2025 | 15561.2 µg/m³ | Northern United States and Canada, May and June 2025 |
| 6 Sept 2023 | 13750.3 µg/m³ | Northern United States and Canada, August and September 2023 |
| 15 Jul 2023 | 13549.5 µg/m³ | United States and Canada, July 2023 |
| 31 May 2025 | 13449.0 µg/m³ | Northern United States and Canada, May and June 2025 |
| 1 Aug 2025 | 12545.2 µg/m³ | North-eastern United States and Canada, 29 July to 9 August 2025 |
| 31 Jul 2025 | 10738.1 µg/m³ | North-eastern United States and Canada, 29 July to 9 August 2025 |
| 15 Jun 2023 | 10436.6 µg/m³ | United States and Canada, June 2023 |
| 14 Jul 2023 | 10236.1 µg/m³ | United States and Canada, July 2023 |
| 16 Jul 2023 | 9834.2 µg/m³ | United States and Canada, July 2023 |
Daily means, the highest since 1 Jan 2023; the WHO's daily guideline is 15 µg/m³. Each date opens that day's world ranking, and each episode the bad-air spell it was part of.
Use this history
SmogRank, PM2.5 monthly and daily means, Watertown, United States, 1 Jan 2023 – 11 Oct 2026. Monitor data from AirNow, via OpenAQ and from the publisher directly; sources listed at smogrank.com/sources. smogrank.com/us/watertown-south-dakota/history (accessed 12 Oct 2026).
You're welcome to reuse a single chart, image or figure with this citation and a link. Terms. Raw monitor readings in bulk are published by OpenAQ, under each provider's licence.
Watertown now: the last 24 hours, its ranks today and the last 12 months day by day.
Updated 2026-10-12 19:07 UTC. Values are PM2.5 (fine particles), the median of each city's monitors, as the US AQI PM2.5 sub-index. Some low-cost readings: Sensor.Community, ODbL (data and licence). Some readings: Uzhydromet (Uzbekistan's Hydrometeorological Service); Department of Environment, Nepal; Vietnam's government monitors; Aurassure; Umhverfisstofnun (Environment Agency of Iceland); RMCAB (Secretaría Distrital de Ambiente, Bogotá); Love My Air (City and County of Denver), no reuse terms published (why we use them).